Target HR when training at a higher altitude

Ok I am not a big poster but have been lurking for a few months, trying to get the courage to ask my question.

Back story: I have been working out with FB since January and have only lost 5 lbs. I am 40+, 10-15 lbs overweight, high blood pressure and work a desk job. Except on weekends I live a pretty sedentary lifestyle. FB and walking the dog a few miles a day are about all the movement I get daily during the week. Currently I am doing the FB Burn Round 2 program (second time though).

I thought the slow weight loss was due to my diet so In February I bought a scale started tracking my calories (1200 + eat back ALL my exercise cals). Then in March I thought maybe I was not working consistently hard enough and over estimating my calories, so I strapped on my fitness watch and heart rate monitor. I found I was under estimating my calories expended. Then in April I thought maybe I was not working out long enough, so I made sure I did all the extra credit associated with the program I also took measurements to help with tracking. So here 4 weeks later driving my self crazy doing ALL of the above and STILL no weight loss but I have lost a few inches. I am working harder than I ever have in my life and I should feel proud of that. I keep telling myself "trust the process", "it is health you are after", "you are loosing inches", etc" but.... I still question am I doing it "right".

I live in a higher altitude maybe I am doing something wrong in the way I train? When I work out my heart-rate monitor logs that my heart rate gets to my MAX 165-183 pretty easy/quickly. So it is hard for me to stay in the fat burning zone. Most my workouts are within my defined zone 4 but frequently tip into my zone 5. When my heart-rate gets in the higher end of my MAX zone I get real light headed and I have to stop and get it back down to zone 4. So for exercises that include HITT, I could be doing this frequently(3-4xs) during the workout. If I try to keep my heart-rate in the "fat burning" zone 3 (128-146 for me) I don't feel like it is challenging or I am working hard (not sweating at all).

When you train at a higher altitude should your target heart-rate zone different? How should I be training to help with fat loss? Maybe I should start running again, it is easier for me to regulate my heart-rate when running. If I do that should I add running onto the days I do FB burn or just shift the program to add 2-3 days of running? When living in a dry environment and higher altitude should I be drinking MORE than 64oz of water?

Pros:

Lost 5 Lbs

Lost inches

Lowered Blood pressure

Getting stronger

Food is on point

Cons:

Still over weight

my pants are still tight :(